Two-dimensional supramolecular honeycomb networks with cavities of an internal diameter of 2.95 nm were formed by the self-assembly of 4,4',4' '-benzene-1,3,5-triyl-tribenzoic acid (BTA) on a Ag(111) surface at room temperature. Annealing to higher temperatures resulted in two sequential phase transformations into closer-packed supramolecular arrangements. The phase transformations are associated with stepwise deprotonation of the carboxylic acid groups. The voids of the honeycomb network of BTA have a suitable size for the construction of hierarchical structures with guest molecules. Single molecules of the macrocyclic compound mt-33 were successfully confined inside 2D nanocavities of the honeycomb networks and released when the phase was transformed to the close-packed structure.

Coordination-based supramolecular chemistry, [1] with its characteristic control of the self-assembly process and intrinsic defect tolerance, has been proven to be a very efficient synthetic tool to fabricate metallosupramolecular networks of well-defined topology in one, two, and three dimensions. [2][3][4][5][6][7][8] This strategy was recently applied to low dimensions by assembling regular molecular architectures from organic molecules and transition-metal centers directly on solid surfaces. [9, 10] A variety of surface-supported molecular network structures has been made accessible by the general application of a surface-assisted metal-coordination method to metal centers and aromatic polycarboxylic acids on metal surfaces. [9] As valid for supramolecular structures in general, the structures of the two-dimensional metal-organic coordination networks (2D-MOCNs) formed are predetermined by the properties of the ligands (e.g., donor atoms and their spatial arrangement, steric crowding) and the electronic characteristics of the metal ions (e.g., involved orbitals, ionization energies). However, under 2D conditions, the realization of a given coordination algorithm might be altered by the presence of a metal substrate, which results in deviating coordination geometries for the same metal-ligand coupling in comparison to the 3D situation (e.g., in the bulk phase). Such deviation can be attributed to charge transfer or screening effects and the strict 2D confinement of ligands and metal centers imposed by the substrate, which substantially influences the characteristics of the metal-to-ligand bonding within the 2D coordination network. [10e]

Hydrogen-bond formation between ionic adsorbates on an Ag(111) surface under ultrahigh vacuum was studied by scanning tunneling microscopy/spectroscopy (STM/STS), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and molecular dynamics calculations. The adsorbate, 1,3,5-benzenetricarboxylic acid (trimesic acid, TMA), self-assembles at low temperatures (250-300 K) into the known open honeycomb motif through neutral hydrogen bonds formed between carboxyl groups, whereas annealing at 420 K leads to a densely packed quartet structure consisting of flat-lying molecules with one deprotonated carboxyl group per molecule. The resulting charged carboxylate groups form intermolecular ionic hydrogen bonds with enhanced strength compared to the neutral hydrogen bonds; this represents an alternative supramolecular bonding motif in 2D supramolecular organization.

Deprotonation of the carboxy groups of 1,3,5‐benzenetricarboxylic acid adsorbed on the Ag(111) surface occurs in the presence of a dilute 2D Cu adatom gas at the surface, while negligible reaction rates occur under similar conditions with Cu in the form of condensed monolayer islands. These results demonstrate that highly mobile adatoms bestow dynamic heterogeneity on materials.

Die Deprotonierung der Carboxygruppen von 1,3,5‐Benzoltricarbonsäure‐Molekülen auf Ag(111)‐Oberflächen verläuft bereitwillig in Gegenwart eines verdünnten Cu‐Adatom‐Gases auf der Oberfläche, während die Reaktion unter ähnlichen Bedingungen, aber mit Cu in Form kondensierter monolagiger Inseln praktisch nicht stattfindet. Die Ergebnisse zeigen, dass hoch mobile Adatome Materialien eine dynamische Heterogenität verleihen können.

No abstract

Coordination-based supramolecular chemistry, [1] with its characteristic control of the self-assembly process and intrinsic defect tolerance, has been proven to be a very efficient synthetic tool to fabricate metallosupramolecular networks of well-defined topology in one, two, and three dimensions. [2][3][4][5][6][7][8] This strategy was recently applied to low dimensions by assembling regular molecular architectures from organic molecules and transition-metal centers directly on solid surfaces. [9, 10] A variety of surface-supported molecular network structures has been made accessible by the general application of a surface-assisted metal-coordination method to metal centers and aromatic polycarboxylic acids on metal surfaces.[9] As valid for supramolecular structures in general, the structures of the two-dimensional metal-organic coordination networks (2D-MOCNs) formed are predetermined by the properties of the ligands (e.g., donor atoms and their spatial arrangement, steric crowding) and the electronic characteristics of the metal ions (e.g., involved orbitals, ionization energies). However, under 2D conditions, the realization of a given coordination algorithm might be altered by the presence of a metal substrate, which results in deviating coordination geometries for the same metal-ligand coupling in comparison to the 3D situation (e.g., in the bulk phase). Such deviation can be attributed to charge transfer or screening effects and the strict 2D confinement of ligands and metal centers imposed by the substrate, which substantially influences the characteristics of the metal-to-ligand bonding within the 2D coordination network.[10e]

Using scanning tunneling microscopy (STM), electrospray ionization mass spectrometry (ESI-MS), and X-ray photoelectron spectroscopy (XPS), we demonstrate that a free [2]catenane consisting of two interlocking 30-membered rings (cat-30) can be deposited on a Ag(111) surface by vacuum sublimation without decomposition. The deposited cat-30 molecules self-organize as ordered dimer chain structures at the surface, presumably via intermolecular π-π stacking. An in situ addition of Cu atoms to the surfaceadsorbed catenanes induces a drastic change in the molecular organization, i.e., from the dimer chain structure to isolated species. The nitrogen core level spectra suggest that the cat-30 phenanthroline units coordinate with Cu, indicating that the free catenane has been transformed into a Cu-complexed [2]catenane. Since it is known that the two interlocked macrocyclic rings of the free ligand cat-30 completely rearrange, i.e., circumrotate, upon complexation to copper, our results reveal that when adsorbed on the silver surface, the two macrocyclic rings of the free [2]catenane can glide within one another so as to generate the corresponding copper complex by in situ Cu complexation.